The invention relates to a new and improved endoscope for internal examination and diagnosis using an ultrasonic sector scanner, especially for transesophageal cardiography. More particularly, the invention is directed to a unique construction of a mechanical sector scanner capsule for mounting at the distal end of an endoscope to enable ultrasonic examination and diagnosis to be performed internally. While the invention is particularly adapted for transesophageal echocardiography, that application should be regarded as advantageous and exemplary only, and not as a limitation of the scope of the invention.
In echocardiography, and other diagnostic practices utilizing ultrasound, it is common to utilize an ultrasound transducer device applied externally to the body for the transmission and reception and acoustic pulses. In the so-called B-mode diagnostic procedures, a designated area of the body is scanned with acoustic pulses, and the echoes from such pulses are displayed in real time on a CRT (cathode ray tube 2) display. These procedures are non-invasive and easily performed, and have become used rather widely in a variety of fields, including cardiology.
One of the limitations of echocardiographic diagnosis, using an external transducer element, is the character of the intervening materials between the transducer and the heart (or other organ) being examined. For example, an externally applied acoustic pulse may be attenuated or distorted by the intervening presence of rib material, air pockets from the lungs, etc. This limits the areas from which the heart, for example, may be effectively acoustically scanned from the exterior of the body. In addition, patients having pulmonary disease or obesity problems may not be capable of useful cardiographic diagnosis by externally applied ultrasound.
Heretofore, it has been proposed to mount ultrasonic scanning devices at the distal end of an endoscope device, which can be inserted into the body. For example, for echocardiography, it has been proposed to insert such an endoscope into the esophagus. By this means, it is possible to locate an ultrasonic scanning device at the level of the heart, within the esophagus, and transmit acoustic pulses laterally into the heart. Because of the close positioning of the scanning device, and the minimum amount of intervening material to be traversed, a sharp, high quality echo image can be obtained. Additionally, using an endoscope with a controllably bendable distal end, it is possible to position the scanning device within the stomach, oriented to direct acoustic pulses upward into the heart from below. This provides a viewing perspective which is not possible to achieve using external transducer devices.
Although the use of a transesophageal endoscope for echocardiography has many obvious advantages over external devices, the actual utilization of such devices has been severely limited by the extremely high cost and/or impracticability of the devices heretofore provided. In general, ultrasonic sector scanners are of two types: Electronically driven arrays and mechanical sector scanners. Array devices are well suited for mounting on an endoscope, because they can be highly miniaturized and have no moving parts. The scanning of an arcuate sector is achieved by sequential or phased activation of individual transducer elements physically arranged to project at different angles over the included sector. With a mechanical sector scanner device, a single transducer element is mounted for controlled, high speed rocking motion, being pulsed repeatedly during each scanning cycle.
While theoretically ideal for endoscope application, the use of array scanners for echocardiography and other end uses has been sharply limited by the prohibitively high cost of such equipment. Mechanical sector scanners, on the other hand, while capable of being produced at only a fraction of the cost of that of an array scanner, have up to now been completely unsuitable for practical clinical use and have been employed, if at all, only under laboratory conditions.
Because space requirements are extremely constrained for an endoscope-mounted transducer suitable for passage through the esophagus, for example, the conventional approach to the utilization of mechanical sector scanners in such applications has involved the use of a drive motor mounted at the proximal (external) end of the endoscope and arranged to manipulate an echo device at the distal end through remote drive means. In some cases, an elongated, rotatable drive shaft has been employed; in others, a string and pulley drive arrangement has been used to transmit motion from the remote drive motor to the internal echo device. In practice, these devices have been of very limited usefulness, because of the inherent error in relating, with the necessary precision, the position of the remote drive motor to the position of the internal echo device. The substantial distance between these two devices allows too much stretch and distortion in the intervening drive means.
One attempt to avoid the problems of the remote drive device is represented by the Suwaki et al. U.S. Pat. No. 4,375,818. There, among a variety of proposals offered, is an arrangement in which a drive motor, gear box and rockable mechanical sector scanner are mounted at the distal end of an endoscope, within an oil-filled bag. Such a device is necessarily large and bulky, and not suitable for general clinical use in transesophageal and similar applications. The size of the device is of obvious importance in that, first, it must easily enter and move through the esophageal passage and, secondly, possible discomfort of the patient must be minimized.
A feature of the present invention is the design and construction of a highly reliable, highly precise mechanical sector scanner device, for endoscope mounting, which is entirely self-contained within an extremely small capsule and thus ideally suited for such applications as transesophageal echocardiography. The device of the invention, produceable at a fraction of the cost of electronic arrays, and altogether free of the important disadvantages of prior mechanical scanner devices, is well suited for general diagnostic use.
Pursuant to the invention, a precision mechanical sector scanner device may be contained in a capsule of approximately one cm in diameter and about three cm in length, ideally suited for attachment to the distal end of an endoscope device.
In accordance with one aspect of the invention, a unique form of mechanical sector scanner device is provided, in which a magnetic rotary element and transducer element are fixed to a common shaft, mounted within an oil-filled, sealed, cylindrical capsule for rotation through a predetermined sector scanning angle. The capsule housing comprises two coaxially aligned tubular housing sections joined end to end. One of the housing sections is formed of magnetic material and surrounds the magnetic rotor, while the other housing section is formed of acoustically transparent plastic material and surrounds the transducer element.
To particular advantage, the common shaft, to which the rotor and transducer means are fixed, is of tubular construction, and flexible conductor wires, for activating the transducer, extend through the center of the shaft. These conductors are connected at their outer ends to the transducer crystal, and at their inner ends to a fixed terminal plate. During sector scanning operations, the motion of these conductor wires is limited to a slight back and forth twisting motion.
Position sensing means is contained within the sealed capsule and provides constant feedback of the exact angular orientation of the transducer crystal. This enables the CRT display to be precisely synchronized with the position of the transducer. Moreover, it enables high precision control over the motions of the crystal during its scanning operations.
As a specific advantageous feature, one end of the transducer capsule is formed by a terminal plate having axially projecting conductor pins electrically connected to the various elements within the capsule. This enables the capsule to be literally "plugged in" to a socket board provided at the distal end of the endoscope device. The device of the invention utilizes a practical minimum number of individual parts and derives an optimum level of performance therefrom. This enables the device to be miniaturized without creating excessive cost in the manufacturing operation or compromising performance.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments of the invention and to the accompanying drawings.